1. Field of the Invention
The present invention generally relates to an image displaying medium on which a composite image constituted of a displaying image and a latent image is displayed, a method of generating composite image displaying data of the composite image and an image generating system.
2. Description of the Related Art
Due to recent technological progress, it has been difficult to distinguish an original from a fake in which contents are added to the original or a part is deleted from the original. In order to surely distinguish the original from the fake, an image processing apparatus which can detect the fake or falsification of the original on a generally used paper has been disclosed (for example, refer to Patent Document 1). In Patent Document 1, letter information and a background pattern are formed in a document. The background pattern is formed depending on the letter information not to contact the letter information. When some information is added to or deleted from the document, the background pattern overlaps the letter information or a blank appears on the document. Therefore, adding or deleting information to/from the original is distinguished.
Documents such as a personal ID card for a company and securities must be prevented from being faked. In these documents, there is a technology in which a latent image appears when a document is duplicated. Specifically, a latent image is formed on an original by using a color which cannot be recognized with the naked eye, and when the original is duplicated, a letter (latent image) showing the duplication is formed on the duplicated paper. As one of the technologies, a dot pattern displaying medium technology which can easily determine whether a document is an original has been disclosed (for example, refer to Patent Document 2). In Patent Document 2, a dot pattern composed of two or more colors having the same pitch as that of lenses of a lens array is formed. A first letter appears when the lens array focuses on a first position and a second letter appears when the lens array focuses on a second position. That is, the first letter and the second letter appear by shifting the position of the lens array. In addition, in a dot pattern composed of mesh points in which the number of screen lines is 300 lpi (line per inch) or more, the dot pattern is blurred when duplicated because the resolution of a generally used duplicating machine is not large enough. With this, it can be determined whether the document is the original or the fake by a letter condition composed of the dot pattern.
[Patent Document 1] Japanese Laid-Open Patent Application No. 2001-358931 (FIG. 4)
[Patent Document 2] Japanese Laid-Open Patent Application No. 2001-324949 (FIGS. 3 and 6)
However, in Patent Document 2, in order to determine whether the document is the original or the fake, a letter must be formed by mesh points of 300 lpi or more. That is, a latent image must be formed by the mesh points of 300 lpi or more. Consequently, costs and man hours are increased because the latent image must be formed by thin mesh points. In addition, it is difficult to form the latent image by a generally used copying machine or printer, and only when a large quantity of a document is formed, the latent image is formed by using a suitable printing machine having the mesh pints of 300 lpi or more. In addition, in Patent Document 2, since it is determined whether the document is the original by using the blurring condition of the dot pattern, a complicated pattern cannot be used because it is difficult to determine whether the appeared pattern is an original pattern or a pattern which is a blurred form of the original pattern.